1. Field of the Invention
The present invention relates to a touch panel. More specifically, the present invention relates to a touch panel-integrated liquid crystal display device wherein a touch panel is formed on the outer side of a substrate in a liquid crystal panel to reduce the total number of substrates used and to optimize the connection between a driving portion of the touch panel and a driving portion of the liquid crystal panel.
2. Discussion of the Related Art
In keeping with dramatic advances in information technology, displays to visualize electric information signals have been rapidly developed. Various slim, lightweight, and low-power flat display devices are commonly used as alternatives to conventional cathode ray tubes (CRTs).
Examples of flat display devices include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), electroluminescent displays (ELDs) and the like. These flat display devices necessarily require a flat display panel to realize an image wherein the flat display panel has a structure in which a pair of transparent insulating substrates is joined such that an inherent luminous or polarized material layer is interposed between the substrates. Among flat display devices, liquid crystal display devices control light transmittance of liquid crystals using an electric field to display an image. For this purpose, an image display device includes a display panel including liquid crystal cells, a backlight unit to irradiate light to the display panel and a driving circuit to drive the liquid crystal cells.
The display panel is formed such that a plurality of gate lines cross a plurality of data lines to define a plurality of unit pixel regions. Each pixel region includes a thin film transistor array substrate and a color filter array substrate that face each other, a spacer interposed between the two substrates to maintain a predetermined cell gap, and a liquid crystal inserted into the cell gap.
The thin film transistor array substrate includes a plurality of gate lines and a plurality of data lines, a thin film transistor formed as a switching device at each intersection between the gate line and the data line, a pixel electrode arranged in each liquid crystal cell and connected to the thin film transistor, and an orientation layer coated on the resulting structure. The gate lines and data lines receive signals from driving circuits through respective pad portions.
In response to scan signals supplied to the gate lines, the thin film transistor transfers pixel voltage signals from the data lines to the pixel electrode.
In addition, the color filter array substrate includes color filters arranged in respective liquid crystal cells, a black matrix to partition the color filters and reflect external light, a common electrode to supply a reference voltage to the liquid crystal cells, and an orientation layer coated on the resulting structure.
The thin film transistor substrate and the color filter array substrate thus separately formed are arranged and then joined such that the two substrates face each other, liquid crystal is injected into a region provided between the substrates and the region is sealed, thereby completing fabrication of the liquid crystal display device.
There is an increasing need for a touch panel wherein a predetermined portion is touched by the hand or a separate input means and additional information can be transferred to the liquid crystal display device in response to the touch. Such a touch panel is adhered to the external surface of a liquid crystal display.
Touch panels are applied to a variety of information-processing systems since they have advantages of simplicity, reliability, portability, possible input of characters without using additional input systems and easy usage.
Depending upon how touch is sensed, touch panels are divided into resistive touch panels in which direct current is applied to a metal electrode formed in an upper or lower substrate and the touched position is determined from the gradient of voltage/resistance, capacitive touch panels in which a predetermined electric current is formed on a conductive film and positions in which voltage variations occur in upper and lower substrates upon touch are thus sensed and electromagnetic touch panels in which LC induced when an electric pen contacts a conductive film is read to sense the touched position.
Among the touch panels, capacitive-type touch panels include a plurality of x electrodes and a plurality of y electrodes that cross each other arranged on a transparent substrate such that an insulating layer is interposed between the x electrode and the y electrode and sense touch by sensing whether or not electric capacity generated between the x and y electrodes is changed.
Depending on the touch sensation type, touch panels are classified into resistive touch panels, capacitive touch panels and infrared (IR) touch panels. In view of factors such as convenience of fabrication and sensitivity, capacitive touch panels attract much attention in small-size models.
Hereinafter, a conventional touch panel-provided liquid crystal display device will be described with reference to the annexed drawings in detail.
FIG. 1 is a sectional view illustrating a conventional touch panel-provided liquid crystal display device.
As shown in FIG. 1, the conventional touch panel-provided liquid crystal display device comprises: a liquid crystal panel 10 including first and second substrates 1 and 2, a liquid crystal layer 3 filled between the first and second substrates 1 and 2, first and second polarizing plates 4a and 4b adhered to the outer surface of the first substrate 1 and the second substrate 2, respectively; a capacitive-type touch panel 20 placed on the liquid crystal panel 10; and a cover glass 30 to protect the top of the touch panel 20.
The first substrate of the liquid crystal panel is provided with gate lines and data lines which cross each other to define pixel regions, a thin film transistor (TFT) formed at the intersection between the gate line and the data line and a thin film transistor array provided with a pixel electrode (not shown) in the pixel region.
The first substrate 1 is further provided at one side thereof with a printed circuit board (PCB) 8 to drive the gate lines and the data lines.
In addition, the second substrate 2 is provided with a black matrix layer, a color filter layer and a common electrode (not shown, Vcom (applied voltage)).
The structure of the touch panel 20 may be varied depending on the operation mode. For example, a capacitive-type touch panel senses touch position via variation in electric capacity, based on capacitance generated between first and second electrodes which cross each other.
In addition, the touch panel 20 is further provided on the side thereof with a touch driving circuit 25 to operate the touch panel.
Meanwhile, a cover glass 30 to protect the touch panel 20 is further provided on the touch panel.
For the afore-mentioned conventional touch panel-provided liquid crystal display, the touch driving circuit 25 for driving the touch panel 20 is separately formed from the PCB 8 for driving the liquid crystal panel 10, and the touch driving circuit 25 and the PCB 8 are connected to the system driving circuit (not shown) in a system including the liquid crystal panel 10, the touch panel 20 and the cover glass 30.
In this case, in order to connect the touch driving circuit 25 and the PCB 8 to a system driving circuit, connectors and areas to mount the same are required. Such mounting areas cause an increase in the size of the periphery. Also, connectors should be separately provided, disadvantageously requiring numerous manual labor-intensive mounting operations.
In addition, the touch panel 20 is provided at the exterior of the liquid crystal panel 10, thus requiring a double-sided adhesive layer between the touch panel 20 and the liquid crystal panel 10. In this case, a process for forming the touch panel 20, apart from the liquid crystal panel 10, and a process for adhering the touch panel 20 to the liquid crystal panel 10 are required, disadvantageously causing an increase in total thickness caused by use of a plurality of substrates and lengthened process period.
In addition, when the cover glass 30 is provided, a double-sided adhesive layer is also provided between the touch panel 20 and the cover glass 30 to join the cover glass 30 to the touch panel 20.
The conventional liquid crystal display device including a touch panel has the following problems.
First, the touch panel and the liquid crystal panel are separately formed and an adhesive layer is interposed between the panels to join the panels. As a result, the total number of glass substrates required is four to five, that is, two substrates for the liquid crystal panel and two substrates for the touch panel and a cover glass, thus making it impossible to reduce the thickness of the liquid crystal display device. That is, for example, the glass substrate is the thickest, about 0.7T (mm), among all of the elements. This is the reason that the glass substrate is used for cover glasses to protect the touch panel, the liquid crystal panel and the touch panel.
Second, the thickness of the touch panel makes direct connection between the touch driving portion circuit and the PCB for driving the liquid crystal panel impossible and connection thereof is separately realized in a system-driving portion, thus making it impossible to realize circuit integration in the device.
Third, an area to mount the touch driving portion circuit and the PCB for driving the liquid crystal panel is required, thus increasing the size of the periphery of the device and decreasing an active area of the device.
Fourth, the driving circuit of the touch panel requires a long wire for connecting the system-driving portion arranged thereunder due to the thickness of the touch panel and the thickness of the liquid crystal panel, thus making it difficult to simplify mounting of the touch driving circuit.